CA1207552A - Compact reflectometer - Google Patents

Abstract

COMPACT REFLECTOMETER
ABSTRACT
A thin, compact reflectometer is adapted to support and position a generally planar test element in a predetermined, generally horizontal plane during usage. The reflectometer includes a light source and a detector having major portions of their respective illumination and detection axes extending generally parallel to a planar reflectometer-positioning portion on one of two major surfaces of the reflectometer.

Description

COMPACT REFLECTOMETER
FIELD OF THE INVENTION
This invention relateæ to a compact r flecto-meter, and particularly to one designed to be used as an analyzer carried by ~ patient.
BACKGROUND OF THE INVENTION
Recent emphasis has been placed upon compact reflectometers that can be used directly by the patient ~s a blood analyzer. PPrticularly such 10 reflectometers are needed by diabetics who take repeated measurements of the glucose levels of their whole blood. Most properlyJ such reading should be taken at regular intervals, wherever the patient finds himself. This is not possible unless the reflec-15 tometer is readily portable. Portability requiresmore than just being lightweight or small--the bulk and shape also dictate whether the reflectometer is convenient to carry. A truly portable and convenient reflectometer would be one which would f1t, for 20 example, in the patient's shirt or coat pocket.
Preferably, such a reflectometer should not be thicker than 2 cm.
U.S. patent No. 4,518,259, issued May 21, 1985 9 by J. W. Ward, en~itled "Light Guide Reflec-25 tometer" describes a reflectometer featuring a lightguide one interior surface of which acts as a mirror to reflect light from a light source to the horizon-tally supported test element. Such m~rrored surface allows the light source to be difiplaced at an angle 30 to, that i6, to one side of, the normal to the test element~ thereby permi~ting some reduction in thick-nes~. However, because the conventional approach has been to "read" the element by detecting radia~ion diffl-sely reflected at 90~ from the test element, the 35 detector of necessity was placed under the test ele-ment. That is, it is conventional to direct incoming llght at an angle of 45 to the test element, and to ;", ~' detect diffusely reflected light at an angle of 90 thereto, i.e., normal to the plane. This angular arrangement eliminates detection of specular reflection, namely that which is reflected at 45. However, such an optical arrangement dictates the placement of the photodetector directly opposite to the supported test element. Although commercially available inexpensive detectors now have a reduced thickness, they still have an appreciable thickness that adds to the thickness of 10 the photometer if the detectors are placed under the examined test element. The added thickness detracts from portability.
However, portability is not the only require-ment. The reflectometer must be one that is otherwise 15 convenient to use, to insure that it will be used as often as is required. Pocket-sized reflec~ometers have been provided with convenient thicknesses by con-structing the axes of the light source and detector to be generally parallel to the planes of the major 20 exterior surfaces (see for example, those described in the owner's Manual of the "Glucoscan" analyzer, a trademark of Lifescan, Inc., Mountain View, California). However, those reflectometers feature a test element that is oriented vertically when the 25 reflectometer is placed in its normal resting position.
Such vertical orientation has disadvantages, since any excess blood or serum sample on the absorbing pad of the test element will run off into the reflectometer and provide possible contamination. As a result, the 30 patient must either blot off the excess, or wait until it is fully absorbed. In either case, the patient experiences an inconvenience. Also reflectometers such as the "Glucoscan" described above require the test element to be properly aligned with a thin, small slot 35 in order to insert the pad into the reflectometer. This can be a difficulty for elderly or infirm patients.
Thus there has been a need, prior to this invention 7 for a compact reflectometer that is Y :~

~20~7552 adapted to read a test element supported in a generally horizontal orientation, and p~rticularly one that ~o supports the element on a readily accessible support ~urface.
SUMMARY OF THE INVENTION
I have discovered that, unlike the above-noted prior reflectometers, the test element can be supported horizontally by the reflectometer during use, ~nd ~till feature a thickness appropriate to fitting the reflecto-meter in a pocke~. The thickness is minimized by orien-ting the l~ght source and the detector ~o that their respective illuminating and detecting axes are each gen-erally parallel to a planar reflectometer-po6itioning portion on one of the two ma~or ~urfaces of the reflectometer.
More specifically, there is provided a compact reflectometer comprising wall means providing two ma~or exterior surfaces which ~re generally planar and parallel, means for supporting a generally planar test element in a predetermined plane of th~ reflectometer, planar meanæ on one of the ma~or 6urfaces for posi-tioning the reflectometer on a rest ~urface during use 60 that the predetermined support plane is generally horizontal, a light source constructed to pro~ect a beam of light centered on an axis of illumin~tion, and light detertor mean~ constructed to receive light centered on an axis of detection. The light source and the detector means are disposed with their exeæ each being generally parallel to the planar posltioning means of one of the ma~or surface6. The reflectometer further includes directing mean~ for directing a) light from the source to the predetermined plane, and b) diffusely reflected light from the predetermined plane to the detector means.
In a preferred embodiment of the invent~on, the aforesaid predetermined plane of support of the te6t ~207ss2 element is also generally parallel to the axes of the light source and the detector means, and the directing means includes a reflecting surface.
Thus, it is an advantage of the present inven-tion that the reflectometer accepts a hori~ontally-positioned test element on a readily-accessible surface, and can have a thickness no greater than 2 cm.
It is a re]ated advantage of the invention that a pocket-sized reflectometer is provided for use as an analyzer, wherein the risk of contamination of the instrument by the patient's sample is substantially reduced.
It is another advantage of the invention that such a reflectometer can include a second ~etector means to function as a reference that is used to control and maintain constant the output of the light source, with-out sacrificing thinness.
It is yet another advantage of the invention that such a reflectometer can include a second light ~ source for illuminating the test element at a different wavelength, without sacrificing thinness.
Other features and advantages will become apparent UpOD reference to the following Description of the Preferred Embodiments, when read in light of the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is an ~sometric view of a reflecto-meter constructed in accordance with the invention;
Figure 2 is a fragmentary plan view of a test element on the supporting surface of the reflectometer;
Figure 3 i8 a fragmentary sectional view taken generally along the line III-III of Fig. 2;
Figure 4 is a fragmentary sec~ional v~ew taken generally along the path IV-IV of Fig. 3, Figure 5 is a fragmentary sectional view taken along the path V-V of Fig. 4;

Figure 6 i8 a ~chematic view of the elec-tronic controls of the reflectometer~ ~nd Figure 7 i~ a 6chemstic view of the signal pro-cessing circuit comprising part of ~uch electronic con-trols.
DESCRIPTION OF THE PREFEE~RED EMBODIMENTS
The invention is hereinafter described particu-larly with respect to the preferred embodiments wherein the reflectometer of the invention i~ used as an an-alyzer of whole blood. The invention further is described in the preferred context of analyzing whole blood for glucose. In addition, the invention i5 useful in analyzing other biological liquids besides whole blood, and for analytes other than glucose. It i 8 fur-ther u6eful as a reflectometer having a u~e other than a~ an analyzer, particularly where there is a need for compactness similar to that in clinical analysis.
Aæ u~ed herein, "biological liquids" means all liquit~ obtained from animals, including whole blood, plasma, serum, ~west, ~pinal fluid and urine, and liquids compatible with these animal liquids, such ~B
control fluids~ æaline solution~ and diluents.
Figure 1 illustrate~ a reflectometer 10 con-structed in accordance with the invention. A housing 12, which can be in one or several pieces, encases optic portion6 30 diæcu~sed in detail hereinafter. The hous-ing features two ma~or exterior surfaces which have ma~or portions 13 and 15, respectively, that are gener-ally planar. Most preferably, portlons 13 and 15 are al~o generally parallel. Aæ used herein, the recitation of a feature of the reflectometer being "generallyparallel" to a ~urface or plane, means being no more than 10 inclined to that ~urface or plane. "MaJor exterior 6urface" herein refer~ to the largest exterior ~urface-A cover 14 for the reflectometer i~ pivotallyattached at 16 and 18 to the housing by conventional ~207552 means. Also included are a microcomputer 20, and input/output devices comprising a keyboard 22 and a display 2~, respectively.
Reflectometer 10 is intended to function wi~h generally planar test elements E that contain all the necessary reagents in dried form in one or more layers, of which layer S is adapted to receive a patient sam-ple. The test elements E and E' are only schematically illustrated in the drawings. Useful test elements are 10 generally described in U.S. Patent Nos. 3~992,158 issued on November 16, 1976 and 4,258,001 issued on March 2~, 1981. Test elements of this type are currently avail-able under the trademark "Ektachem" from Eastman Kodak Company, Rochester, New York. If the analyzer is par-15 ticularly used to assay for whole blood glucose, a pre-ferred test element is the type described in U.S. Patent No. 4,478,944, issued October 23, 1984, by R. Gross et al entitled "Analytical Element Containing a Barrier Zone and Process Employing Same."
More particularly, such a whole blood glucose test element preferably comprises, in sequence, a sup-port zone, a reagent zone, a barrier zone, and a porous sp~eading zone. The most preferred form of such a test element is one in which the zones are in layers, and the 25 barrier layer is a non-porous film comprising a polymer of which from 30 to 95 percent by weight is polymerîzed from a monomer having the structure Rl CH2=C-COOR~ , (I) from 0.25 to 3n% by weight is polymeri7ed from a monomer having the structure i~

il2~7SSX

~3o l ll CH2-C-C A-R4-M, and (II) from O.l to 50% by weight is polymerized from a monomer having the structure RsO

CH2-C-C-0-~6-OH (III) where Rl, R3, and Rs are independently selected from the group consisting of hydrogen and methyl;
R2 is alkyl of from 1 to 16 carbon atoms;
R4 and R6 are independently selected from the group consisting of alkylene groups having from 1 to 6 carbon atoms;
A is -O- or -N

where R7 is hydrogen, alkyl of 1 to 10 carbon atoms, or cycloalkyl of 5 to 10 carbon atoms, and M is NReR9 ~X or S03X, where R8 and R9 are independently selected from the group consist-ing of hydrogen and alkyl of 1 to 4 carbon atoms, and X
is a counterion. Such polymers are in the form of an 2S amine salt or a sulfonate salt. In the case of the amine salt, it is preferred that the salt be the hydro-halide, especially the hydrochloride. Where the poly-merized monomer contains a ~ulfonate group, it will gen-erally be convenient for it to be in the form of an 30 alkali metal salt, such as Na~ or ~, although other salts can be used as long as the monomer retains water solubility. Thus, X can be a positively charged ion such as Na~, ~, or ~ or a negatively charged ion such as chloride, sulfonate, or the like.

~2075~i~

Preferred polymers of the barrier zone of the improved elements for whole blood glucose analysis are synthesized from the ollowing monomers: n-butyl meth-acrylate, 2-methacryloyloxyethyl-1-6ulfonic acid, sodium salt, 2-acetoacetoxyethyl methacrylate, 2-hydroxyethyl methacrylate, 2-aminoethyl methacrylate hydrochloride, and 2-ethylhexyl methacrylate. The preferred polymers include: poly(n-butyl methacrylate-co-2-methacryloyl-oxyethyl-l-sulfonic acid-co-2-acetoacetoxyethyl meth-acrylate-co-2-hydroxyethyl methacrylate) (60/5/10/25, 70/2.5/10/17.5, or 60/10/10/20); poly(2-ethylhexyl meth-acrylate-co-methacryloyloxyethyl-l-sulfonic acid-co-2-acetoacetoxyethyl methacrylate-co-2-hydroxyethyl meth-acrylate) (50/2.5/10/37.5); and poly(n-butyl meth-acrylate-co-2-aminoethyl methacrylate hydrochloride-co-

2-hydroxyethyl methacrylate~ (50/15/35); where the num-bers in parentheses are weight percentages of the mono-mers in the polymerization mixture.
The polymerlzation is generally carried out at a temperature below about 100 C, in a solution in organic solvents, e.g. the lower alcohols, dimethyl sul-foxide, dimethylformamide, and the like, and then, if desired, the polymeric product is dispersed in water.
Latex polymerization can also be employed although the barrier properties of the polymers prepared in this way have been inferior to those obtained using solution polymerization.
The concentration of total polymerizable mono-mer in the polymerization mixture can be varied widely with concentrations up to about 60 percent by weight and, preferably about 20 to about 40 percent by weight, based on the weight of the monomers, plus solvent, being satisfactory .
Suitable catalysts for the polymerization reac-tion include, for example, the free radical catalysts,such as hydrogen peroxide, cumene hydroperoxide, azo ~20~

type initiators, and the like. In redox polymerization systems, conventional ingredients can be employed.
Any conventional microcomputer 20, Fig. 1, key-board 22 or ou~put display 24 is useful, although the S miniaturized types are preferred. For example, a liquid crystal display 24 is preferred. These components are electrically connected in a conventional manner, Fig. 6, through a signal processing circuit ~00 hereinafter dis-cussed.
The various optic portions 30 of one preferred reflectometer, are shown in Figs. 1-5. This embodiment includes light sources 32 and 34 each em~tting a light beam centered on an axis of illumination 35 (Fig. 4), a support groove 36 for supporting horizontally a test element E or E' (Figs. 1 and 2), such groove including a preferably planar support surface 37, a glass plate 38 mounted within housing 12 to provide a window to the element, and a stop surface 39 (Fig. 3) for abutting the test elements. Plate 38 is also preferably planar. A
detector 40 such as a photodiode (Figs. 3 and 4) which detects light along a path that is centered on an axis of detection 41, is included ~o detect diffusely reflec-ted radiation from a supported test element E'. Light source 34 (Figr 4) is preferably identical ~o source 32, except that the two emit light radiation at two differ-ent wavelengths, for example, red and green. Each of the light sources 32, 34 and detector 40 are mounted in appropriately shaped pockets 42, 44 and 48, respec-tively, (Fig. 4), formed within housing 12 adjacent to bottom surface portion 15 of housing 12 (Fig. S).
Preferably, the axes of pockets 42 and 44 are angled at sbout 30 to the axis of pocket 48 (Fig. 4) while forming a common plane with each other and pocket 48.
Most importantly, that common plane i~ generally parallel to major portion 13 of the maior exterior sur-face. That plane most preferably is also generally par-allel to plate 38 (Fig. 3) to insure the axes 35 and 41 ~20755:~

of the light sources and detector are also generally parallel to the plane of the supported test element.
Light sources 32 and 34 most preferably have lens 49 that tend to collimate the light into narrow beams cen-tered on their respective axes 35.
Because of the aforedescribed construction wherein the axes of the light source and detector of the reflectometer are parallel to the supported test ele-ment, a maJor portion of the dimensions that are ordinarily required between the light source or detec-tor, and the test element, extend sideways, parallel to the plane of the test element and to the major exterior planes of the reflectometer, rather than perpendicular to that plane. The thickness of the reflectometer i~
therefore minimized.
The reflectometer preferably also includes a light trap 50, Fig. 47 for receiving light specularly reflected from the test element. Most preferably, light trap 50 compriæes the other light source 34. Similarly, light source 32 acts as a light trap when light source 34 is operative. However, any other light trap, such as a light-absorbing surface, i8 also useful.
Optic portions 30 include reflecting means, which most preferably i6 a reflecting surface 60, Figs.

3-5, for reflecting illuminating radiation along path 62, Fig. 4, from light source 32 onto supported test element E'. Such radiation proceeds from source 35 to a spotS generally designated "X", on surface 60. Most of the radiation is reflected to a spot "Y" generally cen-tered on a supported ~est element, Fig. 5. To BO directthe light from light source 32 to the test element, reflecting surface 60 is mounted within housing 12 so as to form an angle of 45 to surface 37.

~20755Z

Any conventional mirrored or reflective ~urface 60 will suffice, it being preferred that the surface be generally planar. The 45 orientation noted above i6 achieved by rotating the surface about one of its axes 66, Fig. 4.
Optic portions 30 also include, Figs. 3 and 4, a reflecting surface 70 for reflecting some of the dif-fusely reflected light from test element E', along folded path 72 to detector 40. Surface 70 is also dis-posed at an angle of 45 to the plane of surface 37.
It will be appreciated that reflecting surfaces 60 and 70 preferably fall in the same plane.
Because of such mirrored surfaces9 illuminating radia~ion path 62 impinges at X onto surface 60 at angle alpha, Fig. 4, measured from axis 66. Path 62 is reflected up to and through plate 38 to the supported test element at an angle also equal to alpha. Light diffusely reflected from the test element at 90 (i.e., normal therefrom) is then reflected, Fig. 5, by surface 70 along folded path 72 to detector 40. Angle alpha is chosen to be as close to 90 as possible to maximize the light output of the diffuse reflection along path 72, without adding specular reflection to path 72. A par-ticularly useful value for alpha is about 60.
Most preferably, surfaces 60 and 70 comprise a single mirror. Preferably this same mirror provides a surface 80, Fig. 4, to reflect along path 81, specular reflectance from element E' to the light trap 50 formed by light source 34. Alternatively, surfaces 60, 70 and 80 can compr~se ~hree separate mirrors side-by-side.
Because a reflecting surface is used to fold the paths of both the illuminat~ng light and the light diffu~ely reflected from test element E', both the light sources 32, 34 and the detector 40 can be disposed to one side, which is the left side as shown in Fig. 4, of the normal to the plane of element E'. As a result, 1207S5;i~

distance "d", Fig. 5, namely the thickness of the reflectometer measured from support surface 37 to the major planar portion 15 of the bottom wall of housing 12, is minimized since that distance does not have to also include the thickness of the detector. Such dis-tance is, in one example, no greater than 9 mm.
In accordance with another aspect of the inven-tion, a æecond, reference detector 90 is disposed gen-erally opposite to and coaxial with detector 40 to receive a small fraction (e.g., 10~) of the illuminating light that impinge~ on surface 60. As shown, surface 60 is apertured at 96 to allow such small fraction to pass through and towards detector 90 along path 98, Figs. 4 and 5. To allow detector 90 to also receive a portion of the illuminating radiation from light source 34 in a similar manner, Fig. 4, detector 90 is a wide-angle detector such as PIN photodiode VTB 5051 obtainable from VACTEC. Detector 40, for example is a photodiode VTB 1113 obtainable also from VACTEC.
Alternatively, surfaces 60 and 80 are only par-tially silvered at 96, to allow 10% of the illuminating radiation to be transmitted through to detector 90.
As will be readily apparent, light sources 32 and 34 are preferably LED's because of their size. Use-ful examples include those available from So Li Co., forexample a red LED having the designation ESBR/SBR 5501, and a green LED having the designation ESBGtSBG 5501.
To control light sources 32 and 34 by means of detector 90, a signal processing circuit 200 preferably 3~ is prov~ded, Figs. 6 and 7. This circuit receives the signals from both detectors 40 and 90, and controls the voltages applied to light sources 32 and 34. More specifically, circuit 200 comprises, Fig. 6, an ampli-fier, not shown, for the signal generated by detector 40, and an amplifier 202 for reference detector 90. It also comprises the circuitry which provid~s the feedback 20~7 control of each light source. Specifically, it com-prises resistor 205 that converts the current generated by reference detector 90 into a voltage at point A.
This voltage goes to comparator 210, which compares it with the voltage level Vl of a voltage source 215 pre-set at the factory. If the voltage at A i6 less (or greater) than Vl, comparator 210 generates a higher (or lower) voltage to transistor 220 to increase (or decrease) the current drive to the light source 32. A
switch, not shown, connects the appropriate light source to the signal processing circuit 200 as the user switches from one light source to ~he other.
Alternatively, circuit 200 is replaced by a ratio circuit not shown, so that the ratio of the light detected by the reference detector during calibration, to the light detected by the reference detector during the test, is applied as a correction factor, as is well-known.
In another embodiment, not shown, light source 32 and detector 40 are reversed in position, 50 that the illuminating light strikes the supported test element at 9oo .
As will be readily apparent, the dimensions x and y of optic portions 30, Fig. 4, which are the hori-zontal dimensions when in use, are much larger than the third dimension d, Fig. 5. For example, x and y can be about 30 mm and about 34 mm, compared to the 9 mm noted for d above. Because of such dimensions, it is con-templated that the reflectometer containing such optic portions will have a total maximum thickness "t", Fig.
1, between portions 13 and 15 of the exterior surfaces that is no greater than about 1.6 cm, and occupy a total volume no greater than about 1255 cc. Such a thickness and volume make it ideal for carrying in a pocket.

Because planar portion 15 of the bottom wall ~s generally planar to support surface 37, and is itself adapted to rest on a horizontal surface, support surface 37 of the reflectometer is disposed horizontally when in use. The reflectometer is turned on and properly cal~-br~ted. The patient's drop of whole blood iB applied to absorbing surface S of element E' already easily placed in the horizontal position shown in Fig. 5. Cover 14 is then closed, and one or more readings are taken. After use, the patient discards element E' and returns the reflectometer to his shirt or coat pocket, a feature rendered possible by the small size of the reflecto-meter. As a result, the reflectometer reAdily accom-panies the patlent so that regular readings can be taken. Because the test element is read horizontally on a large surface area, the patient has no difficulty in placing the test element in its ready position against stop surface 39.
The invention has been described in detail with 20 particular reference to preferred embodiments thereof, but it will be understood that variations and modifica-tions can be effected within the Rpirit and scope of the invention.

Claims (9)

What is claimed is:

1. A compact reflectometer comprising wall means providing two major exterior sur-faces which are generally planar and parallel, means for supporting a generally planar test element in a predetermined plane of the reflectometer, planar positioning means on one of said major surfaces for positioning the reflectometer on a rest surface, during use, so that said predetermined support plane is generally horizontal, a light source constructed to protect a beam of light centered on an axis of illumination, light detector means constructed to receive light centered on an axis of detection, said light source and said detector means being disposed with said axes each being generally parallel to said planar positioning means, and directing means for directing a) light from said light source to said predetermined plane, and b) diffusely reflected light from said predetermined plane to said detector means.

2. A reflectometer as defined in Claim 1, wherein said predetermined plane of the test element is generally parallel to said axes, one of said major surfaces comprises said posi-tioning means, and said directing means comprises at least one reflecting surface for reflecting light to and from a test element in said predetermined plane.

3. A compact reflectometer comprising means for supporting a generally planar test element in a predetermined plane, planar means on a major exterior surface of the reflectometer for orienting said predetermined plane generally horizontally when said planar means is placed on a rest surface, a light source constructed to project a beam of light centered on an axis of illumination, light detector means constructed to receive light centered on an axis of detection, said light source and said detector means being disposed with said axes each being generally parallel to said predetermined plane, and reflecting means for a) reflecting light from said source to said predetermined plane along a first path, and b) reflecting to said detector means along a second path, only light that is diffusely reflected from a test element in said predetermined plane, whereby the thickness of said reflectometer measured from said predetermined plane is minimized.

4. A reflectometer as defined in Claim 3, wherein said first path strikes said predetermined plane at a non-orthogonal angle and said second path extends orthogonally from said predetermined plane.

5. A reflectometer as defined in Claim 4, wherein said non-orthogonal angle is about 60°.

6. A reflectometer as defined in Claim 3, wherein said reflecting means comprises a single mirror surface disposed to reflect both illuminating light along said first path and diffusely reflected light along said second path.

7. A reflectometer as defined in Claim 3, and further including reference detector means for detecting said light source directly as a reference against which detection by said light detector means is compared, said reflecting means being disposed between said light source and said reference detector means and constructed to pass a fraction of the light received from said light source, to said reference detector means.

8. A reflectometer as defined in Claim 3, wherein the total thickness of said reflectometer, is no greater than 2 cm.

9. A reflectometer as defined in Claim 3, and further including a light trap disposed to receive light specularly reflected by the supported test element from said light source, and a second light source disposed in said trap with an axis of illumination directed at said reflecting means, said second light source emitting light at a wavelength different from said first-named light source.